The objective of this project is to understand what and how movement features are encoded in ensembles of interacting motor cortical neurons. Although previous electrophysiological research has focused on encoding in single motor cortical neurons, very little work has examined whether spatial-temporal patterns of activity emerging from ensembles of interacting neurons encode features of movement planning and execution. To test this hypothesis, high-density electrode arrays will be chronically implanted in primary motor cortex (MI) and dorsal premotor cortex (PMd) from which 100s of single units will be simultaneously recorded while monkeys perform complex visuo-motor tasks with the arm. A continuous random-tracking task and a step random-tracking task are ideally suited to investigate neural encoding because they uncouple the statistical dependencies among many of the relevant motor variables, more thoroughly sample the movement space, and reduce non-stationarities. Forward and reverse correlation, information-theoretic, and decoding methods will be used to analyze the encoding problem as well the information mapping between the two cortical areas. Two specific aims are proposed in this project. First, kinematic and kinetic tuning properties of motor cortical ensembles will be investigated and compared to single neuron tuning functions under different behavioral contexts. The stability of these tuning functions will be examined by applying different external loads to the arm, varying the behavioral mode (freely moving vs. isometric), or changing the posture of the forearm. Second, it will determined whether spatio-temporal patterns within motor cortical ensembles can be elicited by altering the temporal dynamics and predictability of the movement. This work is significant because it will elucidate how groups of interacting cortical neurons control and coordinate complex movements and will provide an important step in understanding how neuronal ensembles in other cortical areas represent other high-level functioning. In addition, this work has direct relevance towards the development of a neuro-motor prosthesis by which paralyzed patients may be able to control external devices by activating their cortex.